It has been known for a long time that silver ion, copper ion, or zinc ion, etc. has antibacterial properties. For example, the silver ion has been widely used in the form of a solution of silver nitrate as a disinfectant or antibacterial agent. However, such a solution form is inconvenient for handling and restricted in use. In order to eliminate these disadvantages, a product in which metal ions are supported in a solid such as zeolite was developed. For example, French Patent Application No. 1,061,158 describes paint for ships containing 20 to 30% by weight of zeolite which is saturated with copper, zinc or silver. In Japanese Patent Publication No. Sho-63-54013/1988, Japanese Patent Application Laid-Open Nos. Sho-63-260810/1988 and Sho-63-270764/1988, there is described a zeolite composition in which antibacterial properties are further improved.
There was proposed antibacterial zeolite which did not discolor by ultraviolet light such as the sunshine with the passage of time (Japanese Patent Application Laid-Open No. Sho-63-265809/1988). This application relates to antibacterial zeolite in which a part or the whole of ion-exchangeable ions in the zeolite is substituted with ammonium ions and antibacterial metal ions and to an antibacterial polymer composition. However, this antibacterial zeolite has some disadvantages. That is, the zeolite is lacking in heat stability when only silvers are supported as the antibacterial metal. The zeolite itself discolors to become mud yellow color when heated to 300.degree. C., particularly when A-type zeolite is used. Therefore, when it is kneaded into a polypropylene resin at a kneading temperature of 240.degree. C., it makes the resin light brown. This disadvantage causes the zeolite to lose its commercial value.
It is known that antibacterial zeolite particles having silicone-type coating may be prepared by treating the antibacterial zeolite particles with a solution of a silicone-type coating agent (Japanese Patent Publication No. Hei-3-80814/1991). In these particles, their hygroscopic property is suppressed to a degree needed. They have hydrophobic property or water repellent property. Accordingly, these particles have an advantage that molding may be advantageously carried out because they do not release water when they are blended with an organic polymer to be molded.